spp 1257 modelling of the dynamic earth from an integrative analysis of potential fields, seismic...

SPP 1257 Modelling of the Dynamic Earth from an Integrative Analysis of Potential Fields, Seismic Tomography and other Geophysical Data

M. Kaban, A. Baranov and M. Rothacher GFZ Potsdam and

H. Schmeling J. W. Goethe University, Frankfurt/M

First Steps Towards 3D Global Density and Dynamic Model of the Crust and Mantle


Main Goals of the Project

1. Integrative density model of the crust and upper mantle1. Integrative density model of the crust and upper mantle..

a. Improvement of the existing global crustal compilation (Central & South Asia).a. Improvement of the existing global crustal compilation (Central & South Asia).

b. Global determination of the lithosphere thickness (Sodoudi and Kind).b. Global determination of the lithosphere thickness (Sodoudi and Kind).

c. Modelling of the lithosphere and upper mantle density structure andc. Modelling of the lithosphere and upper mantle density structure and

computation of the non-isostatic geoid anomalies and dynamic topography.computation of the non-isostatic geoid anomalies and dynamic topography.

2. Construction of a new “snap-shot” dynamic model of the mantle2. Construction of a new “snap-shot” dynamic model of the mantle..

Key issuesKey issues::

a. Modelling of effects of the transition zone boundaries on the geoid anda. Modelling of effects of the transition zone boundaries on the geoid and

dynamic topography.dynamic topography.

b. Considering strong lateral viscosity variations in the mantle.b. Considering strong lateral viscosity variations in the mantle.

3. Modelling temporal geoid variations3. Modelling temporal geoid variations and effects of sublithospheric and effects of sublithospheric convection.convection.


Integrative Model of the Mantle and the Lithosphere(existing background and main problems)

Some of the Key Problems:1. Crust is the most heterogeneous layer in the Earth. It is principal to determine its

effect beforehand using available information. 2. Impact of compositional and temperature variations in the upper mantle is unclear. 3. Gravity effect of the transition zone (potentially very strong) has not identified in the

observed gravity field/geoid.


Improvement of the Global Crustal Model

-1 30 -1 20 -11 0 -1 00 -9 0 -8 0 -7 0 -6 0 -5 0 -4 010

20

30

40

50

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1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0k m

1. Quality of the existing global crustal models do not meet present-day requirements.2. The new global crustal model is principally improved based on high resolution regional

data.

North America (Kaban and Mooney in prep.)

EuCRUST-07 (Tesauro, Kaban and Cloetingh, 2007 subm.)

Main focus Main focus

of this studyof this study


Collection of new data for Central & South Asia


Moho depth - China

Based on the data from (Li, Mooney and Fan ; Based on the data from (Li, Mooney and Fan ; SodoudiSodoudi et al., 2006, 2006; et al., 2006, 2006; HuangaHuanga & & ZhaobZhaob, 2004; , 2004; ChunjuChunju et al. 2005; et al. 2005; ManginoMangino et al., 1999) and more … et al., 1999) and more …


Moho depth – Middle East


Moho depth - India


Modelling of the effect of the transition zone on the geoid and dynamic topography

1. How significant is the impact of the transition zone on the dynamic geoid?

2. Up to now, most of the combined gravity-seismic models are based on the tomography data, in which the effects of velocity variations and phase boundaries are mixed. This can lead to strong artificial seismic velocity anomalies and, consequently, to false inferences on the mantle structure.

3. Artificial “dynamic” reconstructions of the transition boundaries give the topography, which is remarkably different from observations (e.g. Cadek and Fleitout, 1999; Steinberger, 2007).

4. We use the new tomography model of Gu et al. (2003), in which mantle velocities have been estimated in a joint inversion with the transition zone discontinuities.


“Effective” velocity and density variations in the TZ based on traditional tomography models

Parametrization, Gu et al., 2003

In fact, the observed Vs variations could be either negative or positive in the vicinity of the 660 discontinuity depending on many variable factors!

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“Effective” velocity-density scaling factor in the TZ for traditional tomography models

Vertical resolution of the model, kmVertical resolution of the model, km

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New global seismic model based on a simultaneous inversion (660 km)

Ekström and Dziewonski, 1998Gu et al., 2003


Inversion Scheme

To calculate the effect of density variations on the geoid we use a direct method for solution of the differential equation system, which provides a possibility to model arbitrary distributions of density and viscosity with depth (Kaban et al., 2007).


Results of the Simultaneous Inversion(scaling factor)


Variations of the Model Parameters


Observed and Calculated Geoid


Impact of the transition zone boundaries


Summary and Perspectives

1. The global model of the crust is principally improved in several key regions. This model provides a basis for construction of a global integrative density model of the crust and upper mantle.

2. Considering the transition zone provides much better similarity of the calculated and observed geoid relative to the previous tomography models.

a. The calculated scaling factor and density jump for the 400-km discontinuity are very close to the mineral physics prediction.

b. The effective density contrast for the 660, which characterizes its depth variations, is 4 times less than the PREM value. We analyze possible mineral physics applications of this result.

c. In agreement with previous GIA studies, viscosity of the layer right above 660 is remarkably less than of the neighboring layers.

3. More results coming soon!


Thank you!Thank you!

spp 1257 modelling of the dynamic earth from an integrative analysis of potential fields, seismic...

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